Adds the language selection on startup. Old NSIS doesn't support the Unicode and some languages from the list, so the patched version should be built with NSIS >= 3.0.
All languages below are supported by the current version of NSIS, but other languages should be translated manually, and it's more complex work, because it needs an integration with Transifex, new scripts for adaptation, etc. So if we want other languages too it should be in separated proposal with designer discussion.